1. Field of the Invention
Broadly speaking, this invention relates to the transmission and reception of clandestine radio signals. More particularly, in a preferred embodiment, this invention relates to the transmission and reception of clandestine radio signals having dispersed frequency spectra.
2. Discussion of the Prior Art
The ability of the Allies to intercept and decode German and Japanese military communications greatly hastened the end of World War II. With modern computers able to decode almost any coded message, the emphasis has shifted more towards making the transmission itself "invisible" rather than to further improving encryptation techniques.
Clandestine radio transmissions are also useful for person-to-person communications in connection with military operations conducted in built-up areas where the existing natural and manmade radio noise may be used as a cover against signal interception by third parties. Clandestine signals are also useful in Identification Friend or Foe (IFF) applications as they can safely be used without alerting the enemy to their existence or nature. Other applications are the search for, and location of, downed aircraft and airmen, and specialized, information "double talk" transmissions. In this latter application, a clandestine signal is used to notify an authorized clandestine receiving station of the "truth value" of the information transmitted over the regular radio channel which may, incidentally, be operating on the same frequency as the clandestine signal transmitter.